Systems and methods mitigating temperature dependence of circuitry in electronic devices

ABSTRACT

Methods and systems for compensating for temperature variation in the performance of electronic circuits and systems are disclosed. In some embodiments, the systems are configured to store compensation parameters determined in calibration, where the compensation parameters are used by the systems to modify performance. In some embodiments, the systems are part of an automatic test equipment (ATE) system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and is a continuation of U.S. Pat.No. 8,760,180, entitled SYSTEMS AND METHODS MITIGATING TEMPERATUREDEPENDENCE OF CIRCUITRY IN ELECTRONIC DEVICES, issued Jun. 24, 2014,which is incorporated herein by reference.

BACKGROUND

Field

The described technology relates to systems and methods of compensatingfor performance variation of electronic circuits caused by temperaturechanges.

Description of the Related Technology

Automatic Test Equipment (ATE) is a computer based system that tests adevice, known as a Device Under Test (DUT). The ATE can be programmed toprovide power signals, reference signals, and input signals to the DUT.The ATE can also be programmed to receive signals, such as voltages andcurrents, generated by the DUT in response to the input from the ATE.The ATE can compare the received signals with predetermined values todetermine whether the DUT is operating according to specifications.Testing and diagnosing faults with ATE can be performed on wafer die,packaged electronic parts, or electronic systems.

In order for the ATE to generate signals for the DUT and to receive andcompare signals from the DUT, the ATE extensively uses referencevoltages. The reference voltages are generally internal to the ATE andare used by the circuitry of the ATE to generate reference signals andinput signals for the DUT, and to receive and compare output signalsfrom the DUT. Accordingly, accurate reference voltages are veryimportant to the proper function of the ATE.

In general, the circuitry of the ATE and the circuitry used to generatethe reference voltages have performance which is sensitive totemperature. This may be especially problematic because the temperaturewithin the ATE can vary dramatically with, for example, changing ambientconditions and changing power used in various components of the ATEwhich change during its operation. Accordingly, voltages, currents,propagation delays, and other circuit parameter values change during theoperation of the ATE. The temperature dependence of ATE performance canbe a dominant source of ATE inaccuracy.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

Certain inventive aspects include methods and systems for compensatingfor temperature variation in the performance of electronic circuits,such as those used in Automatic Test Equipment (ATE) systems. In someembodiments, the systems are configured to store compensation parametersdetermined in calibration, where the compensation parameters are used bythe systems to modify performance of a reference generator, such as abandgap reference generator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematic view of an embodiment of an ATEsystem.

FIG. 2 is a graph showing output voltage of actual and ideal bandgapcircuits.

FIG. 3 is a block diagram of a reference generator connected with acontrol register.

FIG. 4 is a schematic diagram of an embodiment of a reference generatorwhich is configured to receive a signal from a register.

FIG. 5 is a graph showing temperature dependence of the referencevoltage generated by a reference generator for various signal valuesfrom the register.

FIG. 6 is a flowchart diagram illustrating an embodiment of a method ofcalibrating a reference generator receiving an input value from aregister to modify a reference output.

FIG. 7 is a block diagram schematic view of an embodiment of an ATEsystem.

FIG. 8 is a block diagram of a system which includes a circuit whichoperates according to a reference voltage generated by a referencegenerator.

FIGS. 9A-9C illustrate graphs showing the input/output characteristicsof circuit for various temperatures T0-TN, where the internal controlregister of reference generator is programmed with a different values.

FIG. 10 is a flowchart diagram illustrating an embodiment of a method ofcalibrating a reference generator receiving an input value from aregister to modify a reference signal.

FIG. 11 is a block diagram of a force voltage system which is configuredto generate a voltage for a DUT.

FIGS. 12A and 12B illustrate graphs showing the input/outputcharacteristics of force voltage system for various temperatures T0-TN,where the control register of the reference generator is programmed witha various values.

FIG. 13 is a flowchart diagram illustrating an embodiment of a method ofcalibrating the system of FIG. 11.

FIG. 14 is a block diagram of a measure current system which isconfigured to measure a current applied to DUT.

FIGS. 15A-15B illustrate a graph showing the input/outputcharacteristics of a measure current system for various temperaturesT0-TN, where the control register of the reference generator isprogrammed with various values.

FIG. 16 is a flowchart diagram illustrating an embodiment of a method ofcalibrating the system of FIG. 14.

FIG. 17 is a block diagram of a force current system which is configuredto force a current applied to a DUT.

FIG. 18 is a block diagram of a measure voltage system which isconfigured to generate a voltage for a DUT.

FIGS. 19A and 19B illustrate graphs showing the input/outputcharacteristics of the force voltage system for various temperaturesT0-TN, where the control register of the reference generator isprogrammed with various values.

FIG. 20 is a flowchart diagram illustrating an embodiment of a method ofcalibrating the system of FIG. 18.

FIG. 21A is a block diagram of a programmable propagation delay systemwhich is configured to provide a signal to a DUT. FIG. 21B is aschematic diagram of an embodiment of a propagation delay circuit.

FIGS. 22A and 22C illustrate graphs showing the input/outputcharacteristics of the propagation delay system for various temperaturesT0-TN, where the control register of the reference generator isprogrammed with a various values.

FIGS. 22B and 22D are timing diagrams illustrating the input/outputcharacteristics of the propagation delay system with the controlregister programmed with the various values.

FIG. 23 is a block diagram of a measure voltage system which isconfigured to generate a voltage for a DUT.

FIGS. 24A and 24B illustrate a graph showing the input/outputcharacteristics of the measure voltage system for various temperaturesT0-TN, where the compensation function has various values for one ormore compensation parameters.

FIG. 25 is a flowchart diagram illustrating an embodiment of a method ofcalibrating the compensation function of the system of FIG. 23.

FIG. 26 is a block diagram of a measure current system which isconfigured to generate a voltage for a DUT.

FIGS. 27A and 27B illustrate graphs showing the input/outputcharacteristics of the measure current system for various temperaturesT0-TN, where the compensation function has various values for one ormore compensation parameters.

FIG. 28 is a flowchart diagram illustrating an embodiment of a method ofcalibrating the compensation function of the system of FIG. 26.

DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS

Various aspects and features of methods and devices are described hereinwith reference to the accompanying drawings, which show certainembodiments. The described embodiments may be modified in various ways,without departing from the spirit or scope of the present invention orinventions. In addition, the described embodiments have multiplefeatures and aspects, no single one of which is solely responsible forthe desirable characteristics of the embodiments. Furthermore, no singlefeature or aspect is essential to practicing the methods and systemsdescribed herein. Additionally, various features and aspects of theembodiments may be combined in embodiments not specifically described.For example, one or more features described with reference to oneembodiment may be combined with one or more features described withreference to another embodiment.

Various inventive aspects of certain embodiments of systems and methodsmitigating temperature dependence in electronic circuits are discussed.The aspects, which are discussed herein in the context of ATE devices,may be applied to other electronic devices as well. In some embodiments,the systems and methods provide reference voltages which compensate forvariations in temperature dependencies of the ATE circuitry andreference voltage generation circuitry.

FIG. 1 is a block diagram schematic view of an embodiment of an ATEsystem 10. The various aspects discussed herein in may be applied toother ATE systems and other electronic devices. The ATE system 10 ofthis embodiment is connected to a device under test (DUT) 20 to betested, and includes a DUT power supply (DPS) 30, pin electronics (PE)40, a parametric measurement unit (PMU) 50, a bandgap referencegenerator 60, and a controller 70.

The controller 70 is programmable, and is configured to provide signalsto each of the DPS 30, the PE 40, and the PMU 50 to control theoperation thereof. The controller 70 may be programmed so as to causethe ATE system 10 to provide power and input stimulus to the DUT 20, toreceive electrical responses from the DUT 20, and to compare the DUTresponses with programmed expected values, or test limits. Based on thecomparisons, the ATE system 10 may determine whether the DUT 20functions according to design specifications.

The DPS 30 is configured to provide, for example, power supply voltagesto the DUT 20. The DPS 30 may also be configured to supply referencevoltages and reference currents to the DUT 20. The values of the powersupply and reference voltages and currents may be based on inputreceived from the controller 70.

The PE 40 is configured to provide digital signals to the DUT 20. Forexample, the PE 40 may include or may be connected to a pattern memory,which stores digital data representing signals for the DUT 20. Based onsignals from the controller 70, the PE 40 accesses data from the patternmemory, and provides digital signals to the DUT 20 corresponding withthe digital data in the pattern memory. The timing characteristics ofthe digital signals, for example, the frequency or the duration of thedigital signals may be determined based on signals from the controller70 and the data in the pattern memory.

In this embodiment, the PE 40 is also configured to receive digitalsignals from the DUT 20. For example, the PE 40 may include or may beconnected to a DUT output memory, which stores data representing signalsfrom the DUT 20. Based on signals from the controller 70, the PE recordssignals from the DUT 20, and provides data to the output memoryrepresenting the recorded signals. The timing characteristics of therecorded data, for example, time points when the data is recorded, maybe determined based on signals from the controller 70.

The PMU 50 is configured to determine values of, for example, voltagesand currents output from the DUT 20. Accordingly, the PMU 50 may includeor may be connected to one or more analog to digital converters, whichare configured to receive a voltage or a current from the DUT 20 and togenerate a digital value representing the voltage or current. Thedigital value may then be stored in the DUT output memory. The timingcharacteristics of the measurements, for example, time points when themeasurements are taken, may be determined based on signals from thecontroller 70.

The DPS 30, the PE 40, and the PMU 50 include numerous circuits whicheach use one or more reference voltages or currents to provide accurateand precise performance. In this example, the reference voltages aregenerated based on one or more voltages generated by bandgap referencegenerator 60. In some embodiments, a voltage generator other than abandgap reference generator may be used. [Note: Please list any otherreference generators.]

As discussed above, although reference generators may be designed tominimize temperature dependence, at least because of variations inmanufacturing processes and simulation modeling errors, the referencevoltages or currents also have a nonzero temperature dependence. This isillustrated in FIG. 2, which is a graph showing output voltage of actualand ideal bandgap circuits. Accordingly, the performance of the ATEsystem 10 is dependent on temperature at least because of the nonzerotemperature dependence of the reference generator.

FIG. 3 is a block diagram of a reference generator 100 connected withcontrol register 110. In this embodiment, the reference generator 100 isconfigured to generate reference voltages and/or currents based on inputfrom the control register 110. Each of the possible input values fromthe control register 110 corresponds with a different temperaturedependence of the reference voltage or current from the referencegenerator 100.

FIG. 4 is a schematic diagram of an embodiment of a reference generator120 which is configured to receive a signal from a register 130. In thisexample, reference generator 120 is configured to generate a referencevoltage at output node Vout. The reference voltage has a temperaturedependence which may be modified by changing the signal from theregister 130. The reference generator 120 is an example only, and othergenerators may be used.

In this embodiment, reference generator 120 includes programmablecurrent source 140 and current to voltage converter 150. Current source140 is configured to provide a current to converter 150, which generatesa voltage output based on the current.

Current source 140 is configured to generate the current with atemperature dependence. For example, current source 140 may include acurrent generator (not shown) which has one or more bipolar transistorsand one or more resistors. An increase in temperature causes the currentgenerator to produce less current. The current provided to converter 150may be mirrored from the current of the current generator using acurrent mirror having a reference device and a number of output devices.As a result, the current provided to the converter 150 is the current ofthe current generator multiplied by a factor determined by the relativesize of the reference device and the number and size of the outputdevices. Similar configurations may be found in conventional bandgapreference voltage generators.

The current provided to converter 150 is also based on the signal fromregister 130. For example, the current source 140 may include an inputunit configured to receive the signal from the register 130. The amountof mirrored current may be dependent on the signal. In some embodiments,the number of output devices of the current mirror is controlled by thesignal.

As a result, in such embodiments, the current provided to converter 150is equal to the current of the temperature dependent current generatormultiplied by a factor determined by the signal from the register 130.Thus, the temperature dependence (or the change in the current for achange in temperature) of the current provided to converter 150 is basedon the current generator of current source 140 and on the signal fromthe register.

The current to voltage converter 150 includes an output unit configuredto generate a voltage based on the current received from current source140. The magnitude of the voltage generated for a fixed received currentis dependent partly on temperature. For example, converter 150 mayinclude a resistor having a resistance which is dependent on temperaturesuch that an increase in temperature causes the resistance to increase.

As a result, in such embodiments, the voltage generated by referencegenerator 120 is based on the temperature dependence of the resistor ofthe current to voltage converter 150, on the temperature dependence ofthe current generator of current source 140, and on the signal from theregister 130. Also, because the effect of the temperature dependence ofthe current generator of current source 140 on the output voltage ofreference generator 120 is based on the signal from the register 130,the signal from register 130 affects the temperature dependence of theoutput voltage of reference generator 120.

In some embodiments, other architectures are used. For example, insteadof or in addition to the number of output devices of the current mirrorbeing controlled by the signal of register 130, the resistance of theresistor of current to voltage converter 150 may be controlled by thesignal of register 130. This may be accomplished, for example, by acircuit configured to selectively switch in resistors according to thesignal of register 130. Other programmable voltage reference generatorsmay alternatively be used.

FIG. 5 is a graph showing temperature dependence of the referencevoltage generated by reference generator 120 for various signal valuesfrom the register. As shown in FIG. 5, certain register values result ina reference voltage which increases with an increase in temperature. Inaddition, certain other register values result in a reference voltagewhich decreases with an increase in temperature. An ideal registersetting results in a reference voltage which neither increases nordecreases with an increase in temperature.

FIG. 6 is a flowchart diagram illustrating an embodiment of a method ofcalibrating a reference generator receiving an input value from aregister to modify a reference output. Other methods may alternativelybe used.

At S5, the temperature of the reference generator and surroundingcircuitry is brought to a low value. For example, the junctiontemperature of the reference generator may be brought to 0 C, −20 C, or−40 C. Other temperature values may be used.

At S10, the register is programmed with a value. In response to theregister being programmed, the reference generator receives a signalcorresponding with the programmed value.

In response to the reference generator receiving the signal, thereference generator generates a reference value based on the temperatureand on the seed signal. At S15, the reference value is measured andstored.

At S20, a determination is made as to whether additional values are tobe programmed in the register. If additional values are to be programmedin the register, the method returns to S10. If additional values are notto be programmed in the register, at S25, the temperature of thereference generator and surrounding circuitry is brought to a highvalue. For example, the junction temperature of the reference generatormay be brought to 100 C, 120 C, 140 C, or 160 C. Other temperaturevalues may be used.

At S30, the register is programmed with a value. In response to theregister being programmed, the reference generator receives a signalcorresponding with the programmed value.

In response to the reference generator receiving the signal, thereference generator generates a reference value based on the temperatureand on the received signal. At S35, the reference value is measured andstored.

At S40, a determination is made as to whether additional values are tobe programmed in the register. If additional values are to be programmedin the register, the method returns to S30. If additional values are notto be programmed in the register, at S45, a register value is selected.

To select a register value, the temperature dependence of the referencevalues associated with each register value may be determined bycalculating a difference between the generated reference values for eachregister value at two or more temperatures. The temperature dependencesresulting from the various register values are compared, and theregister value resulting in a minimum reference value temperaturedependence may be selected.

Alternative methods may be used for calibrating the reference generatorand associated register. For example, a binary search algorithm may beused.

FIG. 7 is a block diagram schematic view of an embodiment of an ATEsystem 150. The various aspects discussed herein in may be applied toother ATE systems and other electronic devices. The ATE system 150 ofthis embodiment is connected to a device under test (DUT) 160 to betested, and includes a DUT power supply (DPS) 170, pin electronics (PE)180, a parametric measurement unit (PMU) 190, and a controller 200. TheATE system 150 also includes a reference generator for each of the DPS170, the PE 180, and the PMU 190; and a controller for each of thereference generators. Accordingly, the ATE system 150 includes areference generator 175 for DPS 170, and a controller 177 for referencegenerator 175. The ATE system 150 also includes a reference generator185 for PE 180, and a controller 187 for reference generator 185. Inaddition, the ATE system 150 includes reference generator 195 for PMU190, and controller 197 for reference generator 195

The controller 200 is programmable, and is configured to provide signalsto each of the DPS 170, the PE 180, and the PMU 190 to control theoperation thereof. In some embodiments, the controller 200 functionssimilar to the operation of controller 70 with respect to DPS 30, PE 40,and PMU 50 as described above with reference to FIG. 1. Likewise, DPS170, PE 180, and PMU 190 may respectively function similar to theoperation of DPS 30, PE, and PMU 50 as described above.

The DPS 170, the PE 180, and the PMU 190 each include numerous circuitswhich each use one or more reference voltages to function with accurateand precise performance. In this example, the reference voltages aregenerated based on one or more voltages generated by the respectivereference generators 175, 185, and 195.

As discussed above, although reference generators may be designed tominimize temperature dependence, at least because of variations inmanufacturing processes and simulation modeling errors, the referencevoltages have a nonzero temperature dependence. In addition, each of thecircuits within ATE system 150 similarly functions with a nonzerotemperature dependence. Accordingly, the outputs generated by each ofthe DPS 170, the PE 180, and the PMU 190 vary with temperature at leastbecause of the temperature dependence of the DPS 170, the PE 18, and thePMU 190 themselves, and also because of the temperature dependence ofthe respective reference generators 175, 185, and 195.

In some embodiments, each of the reference generators 175, 185, and 195may be controlled using their respective controllers 177, 187, and 197in a way similar to that described above with respect to referencegenerator 100 and control register 110 of FIG. 3. In such embodiments,each of the reference generators 175, 185, and 195 generate referencevoltages which have minimal temperature dependence.

Alternatively, each of the reference generators 175, 185, and 195 may becontrolled with their respective controllers 177, 187, and 197 so as tominimize the temperature dependence in the output of the circuit forwhich the reference voltages of each of the reference generators 175,185, and 195 are used. Accordingly, in the example ATE system 150,reference generator 175 may be controlled with controller 177 so as tominimize the temperature dependence in the output of DPS 170. Likewise,reference generator 185 may be controlled with controller 187 so as tominimize the temperature dependence in the output of PE 180, andreference generator 195 may be controlled with controller 197 so as tominimize the temperature dependence in the output of PMU 190.

FIG. 8 is a block diagram of a system 210 which includes a circuit 220which operates according to a reference voltage generated by referencegenerator 230. In this example, reference generator 230 includes aninternal programmable control register having functionality similar tocontrollers 177, 187, and 197 discussed above with reference to FIG. 7.In addition to operating according to the reference voltage generated byreference generator 230, the circuit 220 generates an output based on aninput. Accordingly, the circuit 220 generates an output based on aninput and based on the reference voltage generated by referencegenerator 230. Furthermore, because the reference voltage generated byreference generator 230 is dependent on a value programmed in theinternal control register of reference generator 230, the circuit 220generates an output having at least one parameter which is based on theinput and based on the programmed value.

To facilitate this operation, circuit 220 includes an input unitconfigured to receive a reference signal, and an output unit configuredto generate an output, where at least one parameter of the output isdependent at least in part on the reference voltage and is controllablydependent on a temperature. For example, a change in the parameter inresponse to a change in the temperature is based partly on the referencesignal.

FIG. 9A illustrates a graph showing the input/output characteristics ofcircuit 220 for various temperatures T0-TN, where the internal controlregister of reference generator 230 is programmed with a first value. Asshown, the input/output characteristics of circuit 220 varysignificantly with temperature. FIG. 9B illustrates a graph showing theinput/output characteristics of circuit 220 for the temperatures T0-TN,where the internal control register of reference generator 230 isprogrammed with a second value. As shown, the input/outputcharacteristics of circuit 220 vary less with temperature when thereference generator 230 is programmed with the second value than withthe first value. FIG. 9C illustrates a graph showing the input/outputcharacteristics of circuit 220 for the temperatures T0-TN, where theinternal control register of reference generator 230 is programmed witha third value. As shown, the input/output characteristics of circuit 220do not significantly vary with temperature when the reference generator230 is programmed with the third value.

Similar to that discussed above with reference to the referencegenerator of FIG. 4, the temperature dependence of the reference voltageof reference generator 230 is dependent on the programmed value.Accordingly, the temperature dependence of the reference voltagegenerated by reference generator 230 is different for each of the first,the second, and the third programmed values.

To facilitate this operation, reference generator 230 includes an inputunit configured to receive a programmed value, and an output unitconfigured to generate the reference voltage for the circuit 220. Asdiscussed above, the reference voltage is dependent at least in part onthe temperature, and the temperature dependence of the reference signalis based at least in part on the programmed value.

FIG. 10 is a flowchart diagram illustrating an embodiment of a method ofcalibrating a reference generator receiving an input value from aregister to modify a reference signal, where the reference signal isused by a circuit configured to generate an output based on an input andbased on the reference signal. The reference generator and the circuitmay have characteristics of reference generators and circuits describedelsewhere herein. Other methods of calibration may alternatively beused.

At S55, the temperature of the reference generator and the circuit isbrought to a low value. For example, the junction temperature of thereference generator and circuit may be brought to 0 C, −20 C, or −40 C.Other temperature values may be used.

At S60, the register of the reference generator is programmed with acode value. In response to the register being programmed, the referencegenerator receives a signal corresponding with the programmed codevalue. In response to the reference generator receiving the signal, thereference generator generates a reference value based on the temperatureand on the received signal.

At S62, the input of the circuit is set to an input value. In responseto the input value at the input, and in response to the reference valuereceived from the reference generator, the circuit generates an outputvalue, as described above.

At S65, the output value is measured and stored in a memory.

At S67, a determination is made as to whether additional circuit inputvalues are to be used. If additional circuit input values are to beused, the method returns to S62. If additional circuit input values arenot to be used, at S70, a determination is made as to whether additionalcode values are to be programmed in the register. If additional codevalues are to be programmed in the register, the method returns to S60.If additional code values are not to be programmed in the register, atS75, the temperature of the reference generator and the circuit isbrought to a high value. For example, the junction temperature of thereference generator and circuit may be brought to 100 C, 120 C, 140 C,or 160 C. Other temperature values may be used.

In some embodiments, the low or high temperature is set using at leastone of: heating the electronic device in an oven, cooling the electronicdevice in a cooler, operating the electronic device in a power modecorresponding to the temperature to be set, sensing a temperature of thedevice, and adjusting the temperature based on the sensed temperature.

At S80, the register of the reference generator is programmed with acode value. In response to the register being programmed, the referencegenerator receives a signal corresponding with the programmed codevalue. In response to the reference generator receiving the signal, thereference generator generates a reference value based on the temperatureand on the received signal.

At S82, the input of the circuit is set to an input value. In responseto the input value at the input, and in response to the reference valuereceived from the reference generator, the circuit generates an outputvalue, as described above.

At S85, the output value is measured and stored in a memory.

At S87, a determination is made as to whether additional circuit inputvalues are to be used. If additional circuit input values are to beused, the method returns to S82. If additional circuit input values arenot to be used, at S90, a determination is made as to whether additionalcode values are to be programmed in the register. If additional codevalues are to be programmed in the register, the method returns to S80.If additional code values are not to be programmed in the register, atS95, a register value is selected.

To select a register value, the temperature dependence of the outputvalues associated with each register code value for each input value maybe determined by calculating a difference between the generated outputvalues for each register code value at two or more temperatures for eachinput value. The temperature dependence of the output values associatedwith each register code value may be determined by averaging thetemperature dependence of the output values associated with eachregister code value for all input values. The temperature dependencesresulting from the various register values are compared, and theregister code value resulting in a minimum output value temperaturedependence may be selected as the register value.

For example, two input values may have been be used for each registercode value. To calculate a temperature dependence of the output valuesassociated with a particular register code value, a first temperaturedependence is calculated for the first input value by calculating thedifference between the output values generated at the high and lowtemperatures using the first input value. In addition, a secondtemperature dependence is calculated for the second input value bycalculating the difference between the output values generated at thehigh and low temperatures using the second input value. The temperaturedependence of the output values associated with the particular registercode value may then be calculated by averaging the temperaturedependences of the two input values.

Alternative methods may be used for calibrating the reference generatorand associated register. For example, a binary search algorithm may beused. In some embodiments, instead of using the same input values atdifferent register and temperature values, the input value is changed soas to use the same output values at the different register andtemperature values.

FIG. 11 is a block diagram of a force voltage system 250 which isconfigured to generate a voltage for DUT 260. Force voltage system 250may be used, for example, within an ATE system such as ATE system 150 ofFIG. 7. For example, force voltage system 250 may be used in DPS 170 orPMU 190 of ATE system 150.

In this embodiment, force voltage system 250 is configured to generate avoltage for DUT 260 on conductor Force, where the voltage is based on adigital value in programmable control register 270. The digital value ofprogrammable register 270 is passed to DAC 280. The DAC 280 converts thedigital value from the programmable register 270 into an analog valuefor difference amplifier 290.

Difference amplifier 290 receives the analog value from the DAC 280 andreceives the voltage provided to DUT 260 through conductor Sense.Difference amplifier 290 generates a difference voltage based on thedifference between the analog value from the DAC 280 and the voltagereceived through conductor Sense. The difference voltage is provided tomeasure current (MI) circuit 300, which is discussed in more detailbelow. A force voltage is provided to the DUT 260 through conductorForce, where the force voltage is based on the difference voltage fromdifference amplifier 290, and is substantially equal to the analog valuefrom the DAC 280.

In this embodiment, DAC 280 and difference amplifier 290 each receive areference voltage from reference generator 310, where the referencevoltage is generated by reference generator 310 based on a valuereceived from programmable controller 320. Reference voltage generator310 may be similar to other reference generators discussed herein. Insome embodiments, DAC 280 and difference amplifier 290 each receive areference voltage from a different reference generator.

The relationship between each of the DAC 280 and difference amplifier290, and the combination of the reference generator 310 and thecontroller 320 is similar to the relationship between circuit 220 andreference generator 230 as discussed above with reference to FIG. 8.Accordingly, the force voltage system 250 generates an output voltagefor DUT 260 based on the digital value of programmable register 270 andbased on the reference voltage from reference generator 310.

To facilitate this operation, each of the DAC 280 and the differenceamplifier 290 includes an input unit configured to receive the referencevoltage, and an output unit configured to generate an output, where theoutput of each of the DAC 280 and the difference amplifier 290 isdependent at least in part on the reference voltage and is controllablydependent on a temperature. Because the output voltage of system 250 isbased on the output of the DAC 280 and the difference amplifier 290, achange in the voltage output of system 250 in response to a change inthe temperature is based partly on the reference voltage.

FIG. 12A illustrates a graph showing the input/output characteristics offorce voltage system 250 for various temperatures T0-TN, where thecontrol register 320 of reference generator 310 is programmed with afirst value. As shown, the input/output characteristics of force voltagesystem 250 vary significantly with temperature. FIG. 12B illustrates agraph showing the input/output characteristics of force voltage system250 for the temperatures T0-TN, where the control register 320 ofreference generator 310 is programmed with a second value. As shown, theinput/output characteristics of system 250 do not significantly varywith temperature when the control register 320 is programmed with thesecond value.

To facilitate this operation, reference generator 310 includes an inputunit configured to receive a control input, and an output unitconfigured to generate the reference voltage for the DAC 280 and thedifference amplifier 290. The reference voltage is dependent at least inpart on the temperature, and the temperature dependence of the referencevoltage is based at least in part on the control input.

FIG. 13 is a flowchart diagram illustrating an embodiment of a method ofcalibrating system 250. Other methods of calibration may alternativelybe used.

At S55, the temperature of the system 250 is brought to a low value. Forexample, the junction temperature of the system 250 may be brought to 0C, −20 C, or −40 C. Other temperature values may be used.

At S60, the register 320 of the reference generator 310 is programmedwith a code value. In response to the register 320 being programmed, thereference generator 310 receives a signal corresponding with theprogrammed code value. In response to the reference generator 310receiving the signal, the reference generator 310 generates a referencevalue based on the temperature and on the received signal.

At S62, the register 270 is programmed with an input value. In responseto the input value, and in response to the reference value received fromthe reference generator 310, the system 250 generates an output voltage,as described above.

At S65, the output voltage is measured and stored in a memory.

At S67, a determination is made as to whether additional input valuesare to be used. If additional input values are to be used, the methodreturns to S62. If additional input values are not to be used, at S70, adetermination is made as to whether additional code values are to beprogrammed in the register 320. If additional code values are to beprogrammed in the register 320, the method returns to S60. If additionalcode values are not to be programmed in the register 320, at S75, thetemperature of the system 250 is brought to a high value. For example,the junction temperature of the system 250 may be brought to 100 C, 120C, 140 C, or 160 C. Other temperature values may be used.

In some embodiments, the low or high temperature is set using at leastone of: heating the electronic device in an oven, cooling the electronicdevice in a cooler, operating the electronic device in a power modecorresponding to the temperature to be set, sensing a temperature of thedevice, and adjusting the temperature based on the sensed temperature.

At S80, the register 320 is programmed with a code value. In response tothe register 320 being programmed, the reference generator 310 receivesa signal corresponding with the programmed code value. In response tothe reference generator 310 receiving the signal, the referencegenerator 310 generates a reference value based on the temperature andon the received signal.

At S82, the register 270 is programmed with an input value. In responseto the input value, and in response to the reference value received fromthe reference generator 310, the system 250 generates an output voltage,as described above.

At S85, the output voltage is measured and stored in a memory.

At S87, a determination is made as to whether additional input valuesare to be used. If additional input values are to be used, the methodreturns to S82. If additional input values are not to be used, at S90, adetermination is made as to whether additional code values are to beprogrammed in the register 320. If additional code values are to beprogrammed in the register 320, the method returns to S80. If additionalcode values are not to be programmed in the register 320, at S95, aregister value is selected.

To select a register value, the temperature dependence of the outputvoltages associated with each register code value for each input valuemay be determined by calculating a difference between the generatedoutput voltages for each register code value at the two temperatures foreach input value. The temperature dependence of the output voltagesassociated with each register code value may be determined by averagingthe temperature dependence of the output voltages associated with eachregister code value for all input values. The temperature dependencesresulting from the various register values are compared, and theregister code value resulting in a minimum output voltage temperaturedependence may be selected as the register value.

For example, two input values may have been be used for each registercode value. To calculate a temperature dependence of the output voltagesassociated with a particular register code value, a first temperaturedependence is calculated for the first input value by calculating thedifference between the output voltages generated at the high and lowtemperatures using the first input value. In addition, a secondtemperature dependence is calculated for the second input value bycalculating the difference between the output voltages generated at thehigh and low temperatures using the second input value. The temperaturedependence of the output voltages associated with the particularregister code value may then be calculated by averaging the temperaturedependences of the two input values.

Alternative methods may be used for calibrating the system 250. Forexample, a binary search algorithm may be used. In some embodiments,instead of using the same input values at different register andtemperature values, the input value is changed so as to use the sameoutput values at the different register and temperature values.

FIG. 14 is a block diagram of a measure current system 350 which isconfigured to measure a current applied to DUT 360. Measure currentsystem 350 may be used, for example, within an ATE system such as ATEsystem 150 of FIG. 7. For example, measure current system 350 may beused in DPS 170 or PMU 190 of ATE system 150.

In this embodiment, measure current system 350 is configured to measurea current applied to DUT 360 using conductor FV, where the current isbased on a voltage forced at DUT 360. The forced voltage is based on adigital value in programmable control register 370. The digital value ofprogrammable register 370 is passed to DAC 380. The DAC 380 converts thedigital value from the programmable register 370 into an analog valuefor difference amplifier 390.

Difference amplifier 390 receives the analog value from the DAC 380 andreceives the voltage provided to DUT 360. Difference amplifier 390generates a difference voltage based on the difference between theanalog value from the DAC 380 and the voltage applied to DUT 360. Thedifference voltage is provided to measure current resistor 410 and aforce voltage is provided to the DUT 360. A current is provided toresistor 410 based on the difference voltage, the resistance of resistor410, and the force voltage. The current passes through resistor 410 andis applied to DUT 360. A voltage across resistor 410 is generated inresponse to the value of the current. Difference amplifier 400 generatesa current sense signal MI based on the voltage across resistor 410.

Difference amplifier 400 receives a reference voltage from referencegenerator 420, where the reference voltage is generated by referencegenerator 420 based on a value received from programmable controller430. Reference voltage generator 420 may be similar to other referencegenerators discussed herein.

The relationship between the difference amplifier 400, and thecombination of the reference generator 420 and the controller 430 issimilar to the relationship between circuit 220 and reference generator230 as discussed above with reference to FIG. 8. Accordingly, themeasure current system 350 generates current sense signal MI based onthe voltage across resistor 410 and based on the reference voltage fromreference generator 420.

To facilitate this operation, difference amplifier 400 includes an inputunit configured to receive the reference voltage, and an output unitconfigured to generate an output, where the output of differenceamplifier 400 is dependent at least in part on the reference voltage andis controllably dependent on a temperature. Accordingly, because thecurrent sense signal MI is based on the output of difference amplifier400, a change in the current sense signal MI in response to a change inthe temperature is based partly on the reference voltage.

FIG. 15A illustrates a graph showing the input/output characteristics ofmeasure current system 350 for various temperatures T0-TN, where thecontrol register 430 of reference generator 420 is programmed with afirst value. As shown, the input/output characteristics of measurecurrent system 350 vary significantly with temperature. FIG. 15Billustrates a graph showing the input/output characteristics of measurecurrent system 350 for the temperatures T0-TN, where the controlregister 430 of reference generator 420 is programmed with a secondvalue. As shown, the input/output characteristics of measure currentsystem 350 do not significantly vary with temperature when the controlregister 430 is programmed with the second value.

To facilitate this operation, reference generator 420 includes an inputunit configured to receive a control input, and an output unitconfigured to generate the reference voltage for the differenceamplifier 400. The reference voltage is dependent at least in part onthe temperature, and the temperature dependence of the reference voltageis based at least in part on the control input, which, in thisembodiment, is provided by controller 430.

FIG. 16 is a flowchart diagram illustrating an embodiment of a method ofcalibrating system 350. Other methods of calibration may alternativelybe used.

At S55, the temperature of the system 350 is brought to a low value. Forexample, the junction temperature of the system 350 may be brought to 0C, −20 C, or −40 C. Other temperature values may be used.

At S60, the register 430 of the reference generator 420 is programmedwith a code value. In response to the register 430 being programmed, thereference generator 420 receives a signal corresponding with theprogrammed code value. In response to the reference generator 420receiving the signal, the reference generator 420 generates a referencevalue based on the temperature and on the received signal.

At S62, the register 370 is programmed with an input value. In responseto the input value, and in response to the reference value received fromthe reference generator 420, the system 350 generates an current sensesignal MI, as described above.

At S65, the current sense signal MI is measured and stored in a memory.

At S67, a determination is made as to whether additional input valuesare to be used. If additional input values are to be used, the methodreturns to S62. If additional input values are not to be used, at S70, adetermination is made as to whether additional code values are to beprogrammed in the register 430. If additional code values are to beprogrammed in the register 430, the method returns to S60. If additionalcode values are not to be programmed in the register 430, at S75, thetemperature of the system 350 is brought to a high value. For example,the junction temperature of the system 350 may be brought to 100 C, 120C, 140 C, or 160 C. Other temperature values may be used.

In some embodiments, the low or high temperature is set using at leastone of: heating the electronic device in an oven, cooling the electronicdevice in a cooler, operating the electronic device in a power modecorresponding to the temperature to be set, sensing a temperature of thedevice, and adjusting the temperature based on the sensed temperature.

At S80, the register 430 is programmed with a code value. In response tothe register 430 being programmed, the reference generator 420 receivesa signal corresponding with the programmed code value. In response tothe reference generator 420 receiving the signal, the referencegenerator 420 generates a reference value based on the temperature andon the received signal.

At S82, the register 370 is programmed with an input value. In responseto the input value, and in response to the reference value received fromthe reference generator 420, the system 350 generates a current sensesignal MI, as described above.

At S85, the current sense signal MI is measured and stored in a memory.

At S87, a determination is made as to whether additional input valuesare to be used. If additional input values are to be used, the methodreturns to S82. If additional input values are not to be used, at S90, adetermination is made as to whether additional code values are to beprogrammed in the register 430. If additional code values are to beprogrammed in the register 430, the method returns to S80. If additionalcode values are not to be programmed in the register 430, at S95, aregister value is selected.

To select a register value, the temperature dependence of the outputvoltages associated with each register code value for each input valuemay be determined by calculating a difference between the generatedcurrent sense signals for each register code value at the twotemperatures for each input value. The temperature dependence of thecurrent sense signals associated with each register code value may bedetermined by averaging the temperature dependence of the current sensesignal associated with each register code value for all input values.The temperature dependences resulting from the various register codevalues are compared, and the register code value resulting in a minimumcurrent sense signal temperature dependence may be selected as theregister value.

For example, two input values may have been be used for each registercode value. To calculate a temperature dependence of the current sensesignal associated with a particular register code value, a firsttemperature dependence is calculated for the first input value bycalculating the difference between the current sense signals generatedat the high and low temperatures using the first input value. Inaddition, a second temperature dependence is calculated for the secondinput value by calculating the difference between the current sensesignals generated at the high and low temperatures using the secondinput value. The temperature dependence of the current sense signalsassociated with the particular register code value may then becalculated by averaging the temperature dependences of the two inputvalues.

Alternative methods may be used for calibrating the system 350. Forexample, a binary search algorithm may be used. In some embodiments,instead of using the same input values at different register andtemperature values, the input value is changed so as to use the sameoutput values at the different register and temperature values.

FIG. 17 is a block diagram of a force current system 450 which isconfigured to force a current applied to DUT 460. Force current system450 may be used, for example, within an ATE system such as ATE system150 of FIG. 7. For example, measure current system 450 may be used inDPS 170 or PMU 190 of ATE system 150.

In this embodiment, force current system 450 is configured to force acurrent applied to DUT 460 on conductor FI, where the current is basedon a digital value in programmable control register 470. The digitalvalue of programmable register 470 is passed to DAC 480. The DAC 480converts the digital value from the programmable register 470 into ananalog value for difference amplifier 490.

Difference amplifier 490 receives the analog value from the DAC 480 andreceives a feedback voltage from difference amplifier 500. Differenceamplifier 490 generates a difference voltage based on the differencebetween the analog value from the DAC 480 and the feedback voltage. Acurrent is provided to resistor 510 based on the difference voltage, theresistance of resistor 510, and a voltage at DUT 460. The current passesthrough resistor 510 and is applied to DUT 460. A voltage acrossresistor 510 is generated in response to the value of the current.Difference amplifier 500 generates the feedback voltage for differenceamplifier 490 based on the voltage across resistor 510.

In some embodiments, the reference generator for DAC 480 and differenceamplifier 490 and reference generator 520 for difference amplifier 500have each been calibrated in accordance with a method described above.As a result, the force current system 450 is also calibrated. Therefore,in some embodiments, no further calibration is performed.

In some embodiments, the force current system 450 may be used tocalibrate either the reference generator for DAC 480 and differenceamplifier 490 or reference generator 520, where the other of thereference generator for DAC 480 and difference amplifier 490 andreference generator 520 has been previously calibrated. Calibration ofthe reference generator for DAC 480 and difference amplifier 490 orreference generator 520 may be accomplished using a method similar tothe methods described herein.

FIG. 18 is a block diagram of a measure voltage system 550 which isconfigured to generate a voltage for DUT 560. Measure voltage system 550may be used, for example, within an ATE system such as ATE system 150 ofFIG. 7. For example, measure voltage system 550 may be used in DPS 170or PMU 190 of ATE system 150.

In this embodiment, measure voltage system 550 is configured to measurean input voltage from DUT 560. In this embodiment, the input voltage isthe voltage of conductor V_Dut with respect to a voltage on conductorDUT_Gnd. The voltage difference between conductor V_Dut and conductorDUT_Gnd is buffered by difference amplifiers 570 and 580. The bufferedvoltage difference is applied across conductors V-P and V-N for ADC 590.ADC 590 receives the buffered voltage difference and produces an outputvoltage, which is a digital value representing the buffered voltagedifference.

In this embodiment, difference amplifiers 570 and 580 each receive areference voltage from reference generator 610, where the referencevoltage is generated by reference generator 610 is based on a valuereceived from programmable controller 620. Reference voltage generator610 may be similar to other reference generators discussed herein. Insome embodiments, difference amplifiers 570 and 580 each receive areference voltage from a different reference generator.

The relationship between each of the difference amplifiers 570 and 580and the combination of the reference generator 610 and the controller620 is similar to the relationship between circuit 220 and referencegenerator 230 as discussed above with reference to FIG. 8. Accordingly,the measure voltage system 550 generates an output voltage for DUT 560based on the voltage difference between conductor V_Dut and conductorDUT_Gnd, and based on the reference voltage from reference generator610.

To facilitate this operation, each of the difference amplifiers 570 and580 includes an input port configured to receive the reference voltage,and an output port configured to generate an output signal, where theoutput signal of each of the difference amplifiers 570 and 580 isdependent at least in part on the reference voltage and is controllablydependent on a temperature. Accordingly, because the output of system550 is based on the outputs of difference amplifiers 570 and 580, achange in the output of system 550 in response to a change in thetemperature is based partly on the reference voltage.

FIG. 19A illustrates a graph showing the input/output characteristics offorce voltage system 550 for various temperatures T0-TN, where thecontrol register 620 of reference generator 610 is programmed with afirst value. As shown, the input/output characteristics of force voltagesystem 550 vary significantly with temperature. FIG. 19B illustrates agraph showing the input/output characteristics of force voltage system550 for the temperatures T0-TN, where the control register 620 ofreference generator 610 is programmed with a second value. As shown, theinput/output characteristics of system 550 do not significantly varywith temperature when the control register 320 is programmed with thesecond value.

To facilitate this operation, reference generator 610 includes an inputunit configured to receive a control input, and an output unitconfigured to generate the reference voltage for difference amplifiers570 and 580. The reference voltage is dependent at least in part on thetemperature, and the temperature dependence of the reference voltage isbased at least in part on the control input.

FIG. 20 is a flowchart diagram illustrating an embodiment of a method ofcalibrating system 550. Other methods of calibration may alternativelybe used.

At S55, the temperature of the system 550 is brought to a low value. Forexample, the junction temperature of the system 550 may be brought to 0C, −20 C, or −40 C. Other temperature values may be used.

At S60, the register 620 of the reference generator 610 is programmedwith a code value. In response to the register 620 being programmed, thereference generator 610 receives a signal corresponding with theprogrammed code value. In response to the reference generator 610receiving the signal, the reference generator 610 generates a referencevalue based on the temperature and on the received signal.

At S62, the DUT 560 is caused to generate an input value. For example,DUT 560 may be a resistor of a known value, and a current may be forcedthrough the resistor to generate a known voltage input. In alternativeembodiments, a DUT 560 is not used, and instead, the ATE system isconfigured to force a calibrated input voltage value across conductorV_Dut and conductor DUT_Gnd. In response to the input value, and inresponse to the reference value received from the reference generator610, the system 550 generates an output voltage, as described above.

At S65, the output voltage is measured and stored in a memory.

At S67, a determination is made as to whether additional input valuesare to be used. If additional input values are to be used, the methodreturns to S62. If additional input values are not to be used, at S70, adetermination is made as to whether additional code values are to beprogrammed in the register 620. If additional code values are to beprogrammed in the register 620, the method returns to S60. If additionalcode values are not to be programmed in the register 620, at S75, thetemperature of the system 550 is brought to a high value. For example,the junction temperature of the system 550 may be brought to 100 C, 120C, 140 C, or 160 C. Other temperature values may be used.

In some embodiments, the low or high temperature is set using at leastone of: heating the electronic device in an oven, cooling the electronicdevice in a cooler, operating the electronic device in a power modecorresponding to the temperature to be set, sensing a temperature of thedevice, and adjusting the temperature based on the sensed temperature.

At S80, the register 620 is programmed with a code value. In response tothe register 620 being programmed, the reference generator 610 receivesa signal corresponding with the programmed code value. In response tothe reference generator 610 receiving the signal, the referencegenerator 610 generates a reference value based on the temperature andon the received signal.

At S82, an input value is forced across conductor V_Dut and conductorDUT_Gnd. In response to the input value, and in response to thereference value received from the reference generator 610, the system550 generates an output voltage, as described above.

At S85, the output voltage is measured and stored in a memory.

At S87, a determination is made as to whether additional input valuesare to be used. If additional input values are to be used, the methodreturns to S82. If additional input values are not to be used, at S90, adetermination is made as to whether additional code values are to beprogrammed in the register 620. If additional code values are to beprogrammed in the register 620, the method returns to S80. If additionalcode values are not to be programmed in the register 620, at S95, aregister value is selected.

To select a register value, the temperature dependence of the outputvoltages associated with each register code value for each input valuemay be determined by calculating a difference between the generatedoutput voltages for each register code value at the two temperatures foreach input value. The temperature dependence of the output voltagesassociated with each register code value may be determined by averagingthe temperature dependence of the output voltages associated with eachregister code value for all input values. The register code valueresulting in a minimum output voltage temperature dependence may beselected as the register value.

For example, two input values may have been be used for each registercode value. To calculate a temperature dependence of the output voltagesassociated with a particular register code value, with the particularregister code value programmed, a first temperature dependence iscalculated for the first input value by calculating the differencebetween the output voltages generated at the high and low temperaturesusing the first input value. In addition, a second temperaturedependence is calculated for the second input value by calculating thedifference between the output voltages generated at the high and lowtemperatures using the second input value. The temperature dependence ofthe output voltages associated with the particular register code valuemay then be calculated by averaging the temperature dependences of thetwo input values.

Alternative methods may be used for calibrating the system 550. Forexample, a binary search algorithm may be used. In some embodiments,instead of using the same input values at different register andtemperature values, the input value is changed so as to use the sameoutput values at the different register and temperature values.

FIG. 21A is a block diagram of a programmable propagation delay system650 which is configured to provide a signal to DUT 660. Propagationdelay system 650 may be used, for example, within an ATE system such asATE system 150 of FIG. 7. For example, propagation delay system 650 maybe used in PE 180 of ATE system 150.

In this embodiment, propagation delay system 650 is configured toreceive a digital signal on conductor Signal In and provide a delayedversion of the digital signal to DUT 660, where the amount of delay isdetermined by a delay code from programmable register 680.

In this embodiment, propagation delay system 650 includes propagationdelay circuit 670, which receives a reference voltage from referencegenerator 710, where the reference voltage is generated by referencegenerator 710 based on a value received from programmable controller720. Reference voltage generator 710 may be similar to other referencegenerators discussed herein.

The relationship between the propagation delay circuit 670 and thecombination of the reference generator 710 and the controller 720 issimilar to the relationship between circuit 220 and reference generator230 as discussed above with reference to FIG. 8. Accordingly, thepropagation delay circuit 670 generates an output signal for DUT 660based on the signal received on conductor Signal In. The output signalhas a propagation delay which is based on the delay code from register680 and on the reference voltage from reference generator 710.

To facilitate this operation, the propagation delay circuit 650 includesan input unit configured to receive an input data signal, and an outputunit configured to generate a delayed output signal based on the inputdata signal, where the delay of the output signal is dependent at leastin part on the reference voltage and is controllably dependent on atemperature. Accordingly, a change in the delay of propagation delaycircuit 650 in response to a change in the temperature is based partlyon the reference voltage.

FIG. 21B is a schematic diagram of an embodiment of a propagation delaycircuit which may be used as propagation delay circuit 670 inpropagation delay system 650. Other propagation delay circuits mayalternatively be used in propagation delay system 650.

The propagation delay circuit of FIG. 21B includes propagation delaycell 730 and bias generator 740. Propagation delay cell 730 receives aninput signal at In an generates an output signal at Out-N. The delaybetween the input signal in the output signal is determined by biasvoltage Bias1, which is generated by the bias generator 740 and by biasvoltage Bias2, which is generated by reference voltage generator 710.

In this embodiment, propagation delay cell 730 is a current starvedinverter. The inverter is formed by N device 731 and P device 732.Current for the inverter is determined by N devices 733 and 734 and Pdevices 735 and 736. The amount of current provided to the inverter by Ndevice 733 and P device 735 is determined by bias voltage Bias1. Theamount of current provided to the inverter by N device 734 and P device736 is determined by bias voltage Bias2.

Bias generator 740 receives a control signal from the programmableregister 680 and generates bias voltage Bias1 based on the controlsignal. In some embodiments, bias generator 740 includes a number ofbinary weighted P devices (not shown) which each generate a currentbased on one bit of the control signal. The currents of the P devicesare summed into a diode connected N device (not shown), which develops avoltage at its drain-gate node. The developed voltage is provided topropagation delay cell 730 as bias voltage Bias1.

Thus, the amount of current provided to the inverter is determined bybias voltages Bias1 and Bias2, which are respectively generated based onthe control signal and the reference voltage from reference voltagegenerator 710. Therefore, the amount of current provided to the inverteris determined by the control signal and the reference voltage fromreference voltage generator 710

FIG. 22A illustrates a graph showing the input/output characteristics ofpropagation delay system 650 for various temperatures T0-TN, where thecontrol register 720 of reference generator 710 is programmed with afirst value. As shown, the input/output characteristics of propagationdelay system 650 vary significantly with temperature. To furtherclarify, FIG. 22B is a timing diagram illustrating the input/outputcharacteristics of propagation delay system 650 with the controlregister 720 programmed with the first value. Outputs at temperaturesT0, T1, and TN are shown for the input. As shown, the output is adelayed version of the input, where the amount of delay is dependent onboth the delay code from register 680 and on the temperature.

FIG. 22C illustrates a graph showing the input/output characteristics ofpropagation delay system 650 for the temperatures T0-TN, where thecontrol register 720 of reference generator 710 is programmed with asecond value. As shown, the input/output characteristics of propagationdelay system 650 do not significantly vary with temperature when thecontrol register 710 is programmed with the second value. To furtherclarify, FIG. 22D is a timing diagram illustrating the input/outputcharacteristics of propagation delay system 650 with the controlregister 720 programmed with the second value. Outputs at temperaturesT0, T1, T2, and TN are shown for the input. As shown, the output is adelayed version of the input, where the amount of delay is dependent onthe delay code from register 680 and is not dependent on thetemperature.

To facilitate this operation, reference generator 710 includes an inputunit configured to receive a control input, and an output unitconfigured to generate the reference voltage for propagation delaycircuit 670. The reference voltage is dependent at least in part on thetemperature, and the temperature dependence of the reference voltage isbased at least in part on the control input.

FIG. 23 is a block diagram of a measure voltage system 750 which isconfigured to generate a voltage for DUT 760. Measure voltage system 750may be used, for example, within an ATE system such as ATE system 150 ofFIG. 7. For example, measure voltage system 750 or parts of measurevoltage system 750 may be used in DPS 170 or PMU 190 of ATE system 150.

In this embodiment, measure voltage system 750 is configured to measurean input voltage from DUT 760. In this embodiment, the input voltage isthe voltage of conductor V_Dut with respect to a voltage on conductorDUT_Gnd. The voltage difference between conductor V_Dut and conductorDUT_Gnd is buffered by difference amplifiers 770 and 780. The bufferedvoltage difference is applied across conductors V-P and V-N for ADC 790.ADC 790 receives the buffered voltage difference and produces a digitalvalue representing the buffered voltage difference. The digital value isprovided to processor 800

In this embodiment, compensation for variation in the output voltagecaused by temperature variation may be provided by processor 800. Forexample, processor 800 may be programmed with instructions which causethe processor 800 to calculate a compensated voltage value using acompensation function based on the digital value from the ADC 790 andbased on a temperature value from temperature sensor 810. Thecompensation function has one or more compensation parameters which maybe determined using a calibration method. In some embodiments, processor800 is hardwired to perform the calculation, for example, as a fixedcircuit. In some embodiments, the compensated voltage value representsthe measured input voltage as compensated for temperature variation ofthe difference amplifiers 770 and 780. In some embodiments, thecompensated voltage value represents the measured input voltage ascompensated for temperature variation of the difference amplifiers 770and 780 and the ADC 790.

FIG. 24A illustrates a graph showing the input/output characteristics ofmeasure voltage system 750 for various temperatures T0-TN, where thecompensation function has first values for the one or more compensationparameters. As shown, the input/output characteristics of measurevoltage system 750 vary significantly with temperature. FIG. 24Billustrates a graph showing the input/output characteristics of measurevoltage system 750 for the temperatures T0-TN, where the compensationfunction has second values for the one or more compensation parameters.As shown, the input/output characteristics of system 750 do notsignificantly vary with temperature when the compensation parameters ofthe compensation function have the second values.

FIG. 25 is a flowchart diagram illustrating an embodiment of a method ofcalibrating the compensation function of system 750. Other methods ofcalibration may alternatively be used.

At S55, the temperature of the system 750 is brought to a low value. Forexample, the junction temperature of the system 750 may be brought to 0C, −20 C, or −40 C. Other temperature values may be used.

At S62, the DUT 760 is caused to generate an input voltage value. Forexample, DUT 760 may be a resistor of a known value, and a current maybe forced through the resistor to generate a known voltage input. Inalternative embodiments, a DUT 760 is not used, and instead, the ATEsystem is configured to force a calibrated input value voltage acrossconductor V_Dut and conductor DUT_Gnd. In response to the input voltagevalue, with no compensation, the processor 800 generates an outputvoltage measurement.

At S65, the output voltage measurement is stored in a memory.

In some embodiments, a junction temperature is measured and stored in amemory for each stored output voltage measurement.

At S67, a determination is made as to whether additional input voltagevalues are to be used. If additional input voltage values are to beused, the method returns to S62. If additional input voltage values arenot to be used, at S75, the temperature of the system 750 is brought toa high value. For example, the junction temperature of the system 750may be brought to 100 C, 120 C, 140 C, or 160 C. Other temperaturevalues may be used.

In some embodiments, the low or high temperature is set using at leastone of: heating the electronic device in an oven, cooling the electronicdevice in a cooler, operating the electronic device in a power modecorresponding to the temperature to be set, sensing a temperature of thedevice, and adjusting the temperature based on the sensed temperature.

At S82, an input value is forced across conductor V_Dut and conductorDUT_Gnd. In response to the input value, the system 750 generates anoutput voltage measurement, as described above.

At S85, the output voltage measurement is stored in a memory.

In some embodiments, a junction temperature is measured and stored in amemory for each stored output voltage measurement. In such embodiments atemperature value for each temperature set at S55 and S75 is determinedby taking the average of the junction temperatures stored for eachtemperature setting.

At S87, a determination is made as to whether additional input valuesare to be used. If additional input values are to be used, the methodreturns to S82. If additional input values are not to be used, at S95,compensation parameters for the compensation function are calculated.

In some embodiments, the compensation function is linear and theparameters for the compensation function include a gain and an offset.An output voltage measurement for each of two input voltages—highvoltage (hv) and low voltage (lv) may be stored in a memory for each oftwo temperatures—high temperature (ht) and low temperature (lt).Accordingly, four output voltage measurements are stored in a memory:high voltage/high temp (Vhvht), high voltage/low temp (Vhvlt), lowvoltage/high temp (Vlvht), and low voltage/low temp (Vlvlt). For each ofthe four output voltage measurements, an error voltage may becalcaulated: EVhvht=hv−Vhvht, EVhvlt=hv−Vhvlt, EVlvht=lv−Vlvht, andEVlvlt=lv−Vlvlt.

The gain parameter for the compensation function may be a normalizedaverage of the difference in error voltages for the difference intemperatures, where the average is normalized for the difference in thehigh and low voltages. For example, the gain parameter may be calculatedas follows:gain=[[[(EVhvht−EVhvlt)/(ht−lt)]+[(EVlvht−EVlvlt)/(ht−lt)]]/2]/(hv−lv).

The offset parameter for the compensation function may be a normalizedaverage of the 0 degrees error voltage calculated based on each of theerror voltages and the gain, where the average is normalized for thedifference in the high and low voltages. For example, the offsetparameter may be calculated as follows:offset=[[(EVhvht−gain*ht)+(EVhvlt−gain*lt)]/2]/(hv−lv).

Accordingly, given a measured voltage (Vm) at a temperature (T), usingthe compensation function, the processor 800 calculates a temperaturecompensated voltage (Vc) as follows: Vc=Vm*(offset+gain*T).

Alternative methods may be used for calibrating the system 750. Forexample, a higher order compensation function may be calculated andused, where parameters are calculated based on measurements at more thantwo temperatures using, for example, a curve fitting algorithm. In someembodiments, compensation parameters for compensation functions arecalculated and used for different temperature domains or differentoutput voltage domains. For example, a first compensation function maybe used for voltage measurements which are less than 0 volts, and asecond competition function may be calculated and used for voltagemeasurements are greater than 0 volts. Additionally or alternatively, afirst compensation function may be used for temperatures which are lessthan 25 C, and a second competition function may be calculated and usedfor temperatures greater than 25 C.

FIG. 26 is a block diagram of a measure current system 850 which isconfigured to generate a voltage for DUT 860. Measure current system 850may be used, for example, within an ATE system such as ATE system 150 ofFIG. 7. For example, measure current system 850 or parts of measurecurrent system 850 may be used in DPS 170 or PMU 190 of ATE system 150.

In this embodiment, measure current system 850 is configured to measurea current provided to DUT 860 while a voltage is being forced onconductor Force. In this embodiment, the voltage forced on conductorForce is substantially equal to the input voltage Vin, and is generatedby difference amplifier 870. The current provided to DUT 860 bydifference amplifier 870 is sensed by current measurement device 880,which provides an analog signal representing the current to ADC 890. ADC890 provides a digital signal representing the current to processor 900.In some embodiments, current measurement device 880 includes a senseresistor such as resistor 510 discussed above.

In this embodiment, compensation for variation in the digital signalcaused by temperature variation may be provided by processor 900. Forexample, processor 900 may be programmed with instructions which causethe processor 900 to calculate a compensated current value using acompensation function based on the digital value from the ADC 890 andbased on a temperature value from temperature sensor 910. Thecompensation function has one or more compensation parameters which maybe determined using a calibration method. In some embodiments, processor900 is hardwired to perform the calculation, for example, as a fixedcircuit. The compensated current value represents the measured currentas compensated for temperature variation of the current measurementdevice 880. In some embodiments, the compensated current valuerepresents the measured current as compensated for temperature variationof both the current measurement device 880 and the ADC 890. In someembodiments, compensation for temperature variation of the currentmeasurement device 880 in the ADC 890 are separate.

FIG. 27A illustrates a graph showing the input/output characteristics ofmeasure current system 850 for various temperatures T0-TN, where thecompensation function has first values for the one or more compensationparameters. As shown, the input/output characteristics of measurecurrent system 850 vary significantly with temperature. FIG. 27Billustrates a graph showing the input/output characteristics of measurecurrent system 850 for the temperatures T0-TN, where the compensationfunction has second values for the one or more compensation parameters.As shown, the input/output characteristics of system 850 do notsignificantly vary with temperature when the compensation parameters ofthe compensation function have the second values.

FIG. 28 is a flowchart diagram illustrating an embodiment of a method ofcalibrating the compensation function of system 850. Other methods ofcalibration may alternatively be used.

At S55, the temperature of the system 850 is brought to a low value. Forexample, the junction temperature of the system 850 may be brought to 0C, −20 C, or −40 C. Other temperature values may be used.

At S62, the DUT 860 is caused to generate an input current value. Forexample, DUT 860 may be a resistor of a known value, and a voltage maybe forced across the resistor to generate a known current input. Inalternative embodiments, a DUT 860 is not used, and instead, a currentsource is connected to the Force/Sense node. In response to the inputcurrent value, with no compensation, the processor 900 generates anoutput current measurement.

At S65, the output current measurement is stored in a memory.

In some embodiments, a junction temperature is measured and stored in amemory for each stored output voltage measurement.

At S67, a determination is made as to whether additional input currentvalues are to be used. If additional input voltage values are to beused, the method returns to S62. If additional input current values arenot to be used, at S75, the temperature of the system 850 is brought toa high value. For example, the junction temperature of the system 850may be brought to 100 C, 120 C, 140 C, or 160 C. Other temperaturevalues may be used.

In some embodiments, the low or high temperature is set using at leastone of: heating the electronic device in an oven, cooling the electronicdevice in a cooler, operating the electronic device in a power modecorresponding to the temperature to be set, sensing a temperature of thedevice, and adjusting the temperature based on the sensed temperature.

At S82, an input current value is generated. In response to the inputvalue, the system 850 generates an output current measurement, asdescribed above.

At S85, the output current measurement is stored in a memory.

In some embodiments, a junction temperature is measured and stored in amemory for each stored output voltage measurement. In such embodiments atemperature value for each temperature set at S55 and S75 is determinedby taking the average of the junction temperatures stored for eachtemperature setting.

At S87, a determination is made as to whether additional input valuesare to be used. If additional input values are to be used, the methodreturns to S82. If additional input values are not to be used, at S95,compensation parameters for the compensation function are calculated.

In some embodiments, the compensation function is linear and theparameters for the compensation function include a gain and a slope. Anoutput current measurement for each of two input currents—high current(hc) and low current (lc) may be stored for each of twotemperatures—high temperature (ht) and low temperature (lt).Accordingly, four output current measurements are stored: highcurrent/high temp (Ihcht), high current/low temp (Ihclt), lowcurrent/high temp (Ilcht), and low current/low temp (Ilclt). For each ofthe four output current measurements, an error current may becalcaulated: Elhcht=hc−Ihcht, EIhclt=hc−Ihclt, EIlcht=lc−Ilcht, andEIlclt=lc−Ilclt.

The gain parameter for the compensation function may be a normalizedaverage of the difference in error currents for the difference intemperatures, where the average is normalized for the difference in thehigh and low currents. For example, the gain parameter may be calculatedas follows:gain=[[[(EIhcht−Elhclt)/(ht−lt)]+[(EIlcht−EIlclt)/(ht−lt)]]/2]/(hc−lc).

The offset parameter for the compensation function may be a normalizedaverage of the 0 degrees error current calculated based on each of theerror currents and the gain, where the average is normalized for thedifference in the high and low currents. For example, the offsetparameter for the compensation function may be calculated as follows:offset=[[(EIhcht−gain*ht)+(EIhclt−gain*lt)]/2]/(hc−lc).

Accordingly, given a measured current (Im) at a temperature (T), usingthe compensation function, the processor 900 calculates a temperaturecompensated current (Ic) as follows: Ic=Im*(offset+gain*T).

In some embodiments, the current measurement device 880 includes aresistor, and the ADC 890 receives a voltage generated by the resistor,where the voltage is proportional to the current to be measured. In suchembodiments, the parameters for the compensation function may include aneffective resistance of the resistor, where the effective resistance iscalculated based on the measurements of the method of FIG. 28 usingOhm's law.

In such embodiments, the gain parameter for the compensation functionmay be calculated as the average change in resistance experienced forthe high and low temperatures divided by the difference between the highand low temperatures and normalized for the difference in the high andlow currents. In such embodiments, the offset parameter for thecompensation function may be calculated as the average resistance at thehigh temperature minus the gain times the high temperature andnormalized for the difference in the high and low currents.

Alternative methods may be used for calibrating the system 850. Forexample, a higher order compensation function may be calculated andused, where parameters are calculated based on measurements at more thantwo temperatures using, for example, a curve fitting algorithm. In someembodiments, compensation functions are calculated and used fordifferent temperature domains or different output current domains. Forexample, a first compensation function may be calculated and used forcurrent measurements which are less than 0 amps, and a secondcompetition function may be calculated and used for current measurementsare greater than 0 amps.

The methods and actions described above may be performed by a computersystem or a programmable device which accesses instructions forperforming the methods and actions stored on a computer readable medium,such as a memory or another data storage device. The instructions, whenexecuted by the computer system, cause the methods and actions to beperformed. The instructions may be stored in a non-transitory computerreadable medium, such as a memory or data storage device. The computersystem, configured to perform or to be used to perform the methods andactions described above, accesses the instructions to perform themethods and actions.

The various aspects, processes, actions may be performed sequentially orin parallel. For example, a system capable of parallel processing maydivide certain procedures among the available processing devices.

While various aspects, processes, actions, and systems have beendescribed as being included in the embodiments discussed, the variousaspects, processes, actions, and systems can be practiced with certainmodifications. For example, the sequential order of the various aspects,processes, and actions may be modified. In addition, implementationshaving aspects of more than one embodiment may be practiced.Furthermore, implementations having certain aspects omitted may bepracticed.

What is claimed is:
 1. A method of using an electronic tester to performa test on an electronic device under test (DUT), the electronic testercomprising a voltage measurement system configured to generate anelectrical stimulus for the DUT and to generate a compensated valuebased on an input voltage from the DUT and on an input temperature, thevoltage measurement system further comprising a processor configured tocompare the voltage measurement signal with a test limit to determine aresult of the test of the DUT, the method comprising: calibrating thevoltage measurement system, wherein the calibrating comprises: with thevoltage measurement system, applying a first voltage to a calibrationdevice; setting a temperature of the electronic tester to each ofmultiple temperature values; generating a plurality of first measurementvalues, wherein each of the first measurement values is indicative of ameasured voltage at the calibration device corresponding with the firstvoltage at one of the multiple temperature values; storing each of thefirst measurement values; with the processor, generating a firstrelationship, wherein the first relationship describes a differencebetween the first measurement values for a difference in thetemperatures; generating a compensation function based on the firstrelationship, wherein the compensation function describes a compensatedvoltage value based on a measured voltage value and on a measurementtemperature; and storing the generated compensation function; measuringthe input voltage, wherein the measuring comprises: receiving the inputvoltage from the DUT; generating an electronic indication of the inputvoltage, wherein the indication is dependent on the input voltage and onan input temperature; receiving an indication of the input temperature;and with the processor, calculating the compensated value based on theelectronic indication of the input voltage and based on the inputtemperature, wherein the compensated value is calculated according tothe compensation function, wherein the calculated compensated valuerepresents the input voltage, and wherein the compensation functioncompensates for the dependence of the generated indication of the inputvoltage on the input temperature; and comparing the compensated valuewith a test limit to determine a result of the test of the DUT.
 2. Themethod of claim 1, wherein applying the first voltage to the calibrationdevice comprises applying a current to a load resistance, and modifyingthe applied current to cause a specified voltage across the loadresistance.
 3. The method of claim 1, wherein applying the first voltageto the calibration device comprises applying the first voltage using avoltage source.
 4. The method of claim 1, wherein setting thetemperature of the electronic tester comprises at least one of: heatingthe electronic tester with an oven; cooling the electronic tester with acooler; operating the electronic tester with a power mode correspondingto the temperature to be set; sensing a temperature of the electronictester; and adjusting the temperature of the electronic tester based onthe sensed temperature.
 5. The method of claim 1, wherein storing thefirst measurement values comprises sensing signals each corresponding tothe applied first voltage for each of the temperature values and storingthe sensed signals.
 6. The method of claim 5, wherein storing the firstmeasurement values further comprises sensing a digital valuecorresponding to each of the first measurement values and storing thesensed digital values, and wherein generating the first relationshipcomprises calculating a difference between the sensed digital values fora difference in the temperatures.
 7. The method of claim 6, whereingenerating the compensation function comprises: determining an offset tomultiply the indication of the input voltage by in order to generate ameasurement value dependent offset term; and determining a gain by whichto multiply the measurement temperature and the indication of the inputvoltage by in order to generate a measurement value and temperaturedependent term to be added to the offset term to calculate thecompensated value.
 8. The method of claim 1, further comprising:applying a second voltage to the device at each of the temperatures;generating a plurality of second measurement values, each indicative ofa measured voltage at the calibration device corresponding with thesecond voltage at one of the multiple temperature values; storing eachof the second measurement values; generating a second relationship,wherein the second relationship describes a difference between thesecond measurement values for a difference in the temperatures; whereinthe compensation function is generated based additionally on the secondrelationship.
 9. The method of claim 8, wherein generating thecompensation function comprises: determining an offset to multiply theindication of the input voltage by in order to generate a measurementvalue dependent offset term; and determining a gain by which to multiplythe measurement temperature and the indication of the input voltage byin order to generate a measurement value and temperature dependent termto be added to the offset term to calculate the compensated value.